I think the wikipedia drawing is slightly better than Lightning Mate's (no offence meant, professor) in that it shows the
three-dimensional aspect of what goes on:
http://upload.wikimedia.org/wikipedi...Dihedral_3.png
A side-slip means the aircraft axis is slightly twisted relatively to the flight path, and it is that twist, or divergence from parallel between the relative wind and the airplane centerline, that (if the wing has a dihedral angle) presents the lowered wing to the air in such a way as to increase angle of attack to the oncoming (forward movement) airstream, while reducing AoA for the raised wing.